Method of making strong, thin, cemented carbide disks



July 11, 1933. G.'F. TAYLOR METHOD OF MAKING STRONG, THIN, CMENTED,CARBIDE DISKS Filed sept.v 8'," v195o wmmm |.i4 will@ l Il.

Inventor: George FITQSIOY;

His Attorheg.

Patented July ll, 1.933

GEORG-E F. TAYLOR,

on N'ISKAYUNA', NEW YORK, AssIGNoR 'ro GENERAL ooMPANY, A coRPoRATIoN orNEW Yonx ELECTRIC METHOD oF MAKING STRONG, THIN, CEMENTED oARBipEDIsxsApplication md september s, 193e. serial No. 430,330.

The present invention relates to the manufacture of strong, thin,fine-grained, cemented carbide disks, and particularly to disks of thischaracter which have a central opening therethrough and are suitable foruse as glass cutters and the like. Cemented carbide compositions arewell known and are disclosed in Schrter Patents .#1,549,615 and#1,721,416. Such compositions generally consistof a sintered mixture ofa carbide for example tungsten carbide, with a cementing or bindermedium which has alower melting point than the carbide, for examplecobalt, the cobalt usually comprising from about 3 to about ofthe'composition with the remainder tungsten carbide. While tungstencarbide and cobalt provide the preferred composition other carbides`such as molybdenum carbide and other binder elements such as nickel,iron, manganese and uranium I may be employed if desired.

Heretofore cemented carbides have been employed extensively as bits forcutting tools.' Such bits are relatively thick and mounted on suitablesupporting Shanks.

Whileattempts have been made to manufacture thin cutting disks of theorder of -llg inch in thickness or less from this material, it has beenimpossible prior to the present invention, to produce a satisfactory,tough,

fine-grained disk which Awould be fiat andA capable of ltaking a smooth,sharp, cutting edge when unsupported in a lateral direction. i

Cemented carbide is ordinarily somewhat brittle but when formed intovery thm secy tions, it is so brittle that it is practically impossibleto grind such a disk to astine, smooth cutting edge.l In addition tobrlttleness, it is dithcult to produce 'very thin plates of cementedcarbide thaty will lie perfectly ilat. Very thin plates of this materialwhether produced by squirting or by the process outlined in the aboveSchrter patents are somewhat porous and coarsegrained and have atendency to becomev warped when red at the sintering temperature. Ifthin plates are made by the hotpress methods disclosed in the copendingapplication of Samuel L. Hoyt, Serial N 0.181,-

composition.

536, led A ril 6, 1927 and in Gilson Patent No. 1,7 56,85 such platesare brittle and also coarse grained.

In the prior processes for making cemented carbide, the powderedmaterials from -which the cemented carbide is made is usually in directcontact for an appreciable periodbf timeeither with a carbon boat ormold during the sintering operation. It is my present opinion thatthis'contact with o0 carbon for an appreciableltime at a hightemperature'is themain cause of the brittleness and coarse-grainedstructure'found in very thin plates formed by prior; processes.'Graphite ,has a tendency tov absorb cobalt at o5 the sinteringtemperature of cemented tungsten carbide and this action tends toincrease the brittleness of the cemented material. Coarseness of thefgrain structure also has the same effect and this latter condition is afunction of the time during which the cementing material is heated atthe sintering temperature.

In my copending application Serial No. 363,079, filed May 13, 1927, Ihave disclosed J5 a method for producing thin plates of ce- 'mentedcarbide which are supported laterally by substantially coextensivemolybdenum plates. When the sintered plates are supported, as disclosedin the above application, it is possible to produce a sharp cutting edgeon the disk. The method disclosed in my prior application however is notsuitable Afor the production oflaterally unsupported thin plates ofcemented carbide of. the type described in the present application.

In my prior application, Serial No. 462,368, filed June 19, 1930,1` havedisclosed an apparatus whereby a hard, tough and unusually fine-grainedcemented carbide 90 may be produced by simultaneously applying heat andpressure in a vacuum to powdered materials comprising a hard `metal lemploy the apparatus disclosed in the latter application in carrying outthe present invention.

It is an object of the present invention to provide an improvedmethodyfor producingl thin, cementedcarbide disks which are capable ofoperation without lateral support.

understood from reference to the following specification when consideredin connection with the accompanying drawlng 1n which Fig-1 represents aview partly in sectionv and partly 1n elevation of an apparatus wherebymy invention may be carried into effect. Fig. 2 is a view partly insection and partly in elevation on an enlarged scale of a portion of theapparatus disclosed in Fig. 1, while Figs. 3 and 4 are detail views ofportions of the apparatus disclosed in Fig. 1.

` ,per end' of the plug 4. TheA closure member 2 is provided with acentral upwardly extending guide portion 9 adapted to accommodate amovable rod 10. The rod 10 is provided at its lower end with anextension 10 and carries at its upper end a iatm'etal plate 11 lprovidedwith an extension 12. Plate 11 is of smaller diameterthan closure member2 and isconnected to the latter by means of a corrugated flexible member13;. commonly known as a sylphon bellows. The portion of the member 2which separates the interior of the sylphon from the interior ofreceptacle 1 is perforated with holes 14 whereby the pressure within thesylphon bellows 13 and the receptacle 1 may be equalized.

Pressure may be applied to the plate '11 through a lever 15 pivoted to astandard 16 and provided'with a depending portion 17 which is pivotcd`to lever 15 and. adapted to engage the extension 12 on plate 11. Aweight (not shown) may be positioned at any desired point along` thelever 15 in order to apply a suitable pressure to the plate 11.

If desired, however, the standard 16 and lever 15 may be omitted andpressure apas hereinafter disclosed.

In fabricating .small cemented carbide metal cutting disks, for exampledisks about 0.15 inch in diameter, a hard glass tube 18 is employed asthe mold, the latter having substantiallyeo|ual` to the diameter of thedisks to be fabricated,

a wall thickness of about 1/8 inch or greater, and a length of about 4inches or less. Plungers 19 and 20. made of iron or steel or othersuitable metal, are mounted in opposite ends of the mold 18. Theplungers are each about 2 inches long and provided with central holes 21and 22' respectively. These holes extend in a lengthwise or axialdirection about one-half way through the plungers andA accommodate aremovable or temporary plug 23, about 30 mils in diameter, which ispreferably made of quartz but may be made of graphite.

' In carrying out my invention, the tubular glass mold 18 is loaded byplacing it in a vertical position, inserting the lower plunger 20ltherein to the extent of about lg inch, then fixing the graphite rod 23in the hole 22 of the plunger. 24 having a central opening therein ofthe same diameter as the graphite rod 23 is slid vover the rod 23 so asto rest on the upper end of the plunger 20. Pulverized cemented tungstencarbide 25, for example a powdered mixture consisting of about 13%cobalt and about 87% tungsten carbide in suiiicient quantity Atoproducea sintered disk of about 1/64 inchY thick and about 0.15 inch diameter,is weighed out and placed on the graphite disk 24. The powdered materialin the. mold 18 until the latter is filled to the desired extent.Plunger 19 is then inserted in the upper end of the mold and the latterpositioned in receptacle 1 between cxtensions 8 and 10 as indicated inFig'. 1. The extensions 10 and 8 are provided with adjustable bearingsleeves 26 and 27 respectively which accommodate the out/er ends of theplungers 19 and 20 and center mold 18 in receptacle and h'old theplungers rigidly in such .positions that their axes always fall alongthe same line. Bearing sleeves 26 and 27 may be constructed withopenings of various diameters extendingl therethrough and may beemployed to accommodate any desired diameter of plunger.

When the mold. 18 has been placed in position, the receptacle 1 isflushed out with plied to plate 11 `by the atmosphere only,

hydrogen which may be supplied through the 'opening 5 in the plug 4.After the hydrogen supply is cut off the receptacle is A thin, graphitedisk of current supply (not shown) connected to the plug 4 and to theextension 12. This current is of suliicient intensity to heat theseveral layers of powdered materials 25 to to theirsinteringtemperature. The powdered materials are heated almost instantly tothedesired temperature and as they become heated plunger 19 descends andthepowdered materials are compressed i11- to a hard, tough, metalliccomposition which is uniformly fine-grained and capable of taking a verytine smooth cutting edge.

If a glass tube employed as the mold, the process may be observedclearly. YVhen the electric circuit 1s closed, the graphite disks withinthe mold are hea-ted' to a visible redness increasing to.incandescenee`In the meantime the sections 4of mixed tungsten carbide and cobaltpowders are heated to their sintering temperature partly by radiationfrom the carbon disks and part-ly by the electric current which flowsthrough the 1 powdered material. At the instant when the variousseparate portions of powdered material arrive at their sinteringtemperature, each portion is simultaneously compressed to about one-haltits original thickness. lThis compression of all the disks is completedin merely a fraction of a second. The electric heating circuit is thenopened and hydrogen gas readmitted to the receptacle 1. 'lhemold i8 andplungers 19 and 2() are removed from receptacle 1 and while still hotplunged into water thereby breaking the mold and permitting removal ofthe pressed disks.

Ordinarily, atmospheric pressure alone is sutlicient to compress thepowdered material to the desired thickness. This pressure however may besupplemented by pressure applied to the lever 15. As in my .copendingapplication Serial-No. 462,368, the heating current may, if desired, besupplied to the pressed materialfor a predetermined length of time afterthe powdered materials have4 been pressed to the desired thickness, thecircuit being controlled, as in the prior application, by a switch. 28-mounted on the outer end of lever 15.

Since mold 18 is' electrically non-conducting, it is practically a coldmold'and there- `fore a very high pressure may be applied'to thesintered material. Moreover, since the powdered materials are heated foran unusushort period of time, for example for about 1/300th or 1 500thofthe time required .to hot press similar powdered materials aceordingtothe process disclosed in the above Hoyt application or Gilson patent,there is practically no opportunity either for grain growth in thepressed material or for absorption of cobalt by the carbon disks. As aresult, a very. hard, tough and uniformly {ine-grained product isObtained which mayv be supplied with a smooth keen cutting edge.

Cutting disks produced according to my process have a hardness of aboutto 92 on the Rockwell A scale. lVhile these disks may be supplied with akeen smooth cutting edge, this cannot ordinarily be done with the usualgrinding apparatus but may be accomplished by a grinding wheel made ot'a mixture of cemented tungsten carbide and diamond powder as disclosedin my copen-ding application Serial No. 357,536, l'iled April 23, 1929.`

The small graphite disks may be prepared by cutting off sectionsotsuitable thickness i rom a graphite rod ot the same diameter. Thegraphite disks keep the siutered disks separate from one another andalso prevent plungers 19 andl 20 from sticking to the pressed material.

` Instead of weighing the separate portions 25 of mixed powderedmaterials so as to obtain an exact quantity of material in each disk, Imay squirt a tube-made from a suitable mixture Y of tungsten carbide,cobalt and starchpaste, remove the .paste by firing in hydrogen and thencut equal lengths of the tube and separate them, if desired, with paper.The latter may be reduced to carbon by charring, the heat for the latterpurpose being furnished by the central graphite rod when heated by theelectric current supplied through plug 4 and extension 12.

Although I have illustrated my invention in connection with cementedtungsten carbide,'it is not limited to that material alone. For example,I may hot press in a similar manner `a mixture 'of diamond dust andcemented tungsten carbide such as disclosed Vin thc copendingapplication 'Serial No.

357,536 and form for example disk saws as thin aslg inch and l@ inchdiameter. While such 'material is not as strong as cemented tungstencarbide alone, its strength may be materially increased by the additionof small molybdenum wires thereto. These wires should be about 0.010inch in diameter and preferably in the shape of a Cor O should give itan eiiiciency far exceeding that of any small abrasive saw now in use.Small molybdenum wires may also if desired be added to the cementedtungsten carbideJ powdered materials' in the proportions inicated above.The molybdenum wires Vin either case act to reinforce the pressedowdered material in much the same way that steel reinforces concrete.

What I claim as new and desire to secure by Letters Patentof the UnitedStates, is:

' 1. The method of producingthin metallic verized mixture of tungstencarbide and.

cobalt between two layers of carbonaceous material in an electricallynon-conducting mold, placing said mold in a receptacle, evacuating thereceptacle, completing an electric circuit through the pulverizedmaterial to thereby heat it to itssintering temperature andsimultaneously applying pressure thereto, said circuit being maintainednot more than a .few seconds.

3. The method of simultaneously making a plurality of thin, cementedcarbide disks which ,comprises placing alternate layers of carbon disksand powdered material comprising said carbide in an electricallynonconducting mold, placing said mold in a receptacle, evacuating saidreceptacle,- completing an electric circuit through said layers tothereby heat the powdered material to its sintering temperature,maintaining said circuit for a few moments, and simultaneline-grainedously applying pressure to the material in said mold.

4. The method for making a plurality of thin, cemented carbide diskswhich comprises placing a layer of powdered material comprising saidcarbidevin an electrically non-conducting mold, levelling said powderedmaterial, superimposing a layer ofcarbonaceous material on said powderedmaterial, lling said mold to a desired extent with alternate layers ofsaid powdered material and carbonaceous material, positioning said moldima receptacle, evacuating said receptacle, passing an electric currentthrough said powdered and carbona-I.r ceus materials to thereby heat thepowtemperature, pressure to dered material to its sintering andsimultaneously applying the material in said mold.

5. In combination, a mold, a pair of oppositely disposed plungersmounted in the mold, means for positioning said mold and plungers in areceptacle, said means comprising a member with an opening therein toaccommodate one of saidV plungers and an oppositely disposed movablemember adapted to'accommodate the other of said plungers, said memberseach comprising an adjustable bearing sleeve engaging one ofsaid'plungers. f

In witness whereof, I have hereunto set my hand this 6th day ofSeptember, 1930. GEORGE F. TAYLOR.

